1. Field of the Invention
The present invention relates to an ink to correct a micro defect in a colored pattern, wherein the ink is used for correcting a small defect portion (imperfect portion) in a given colored pattern formed on a substrate, and a correcting method using the same. The present invention also relates to a color filter corrected by using the ink. Further, the present invention relates to a suitable process for producing the ink to correct a micro defect in a colored pattern.
2. Description of the Related Art
When a small colored pattern having a given color such as R (red), G (green), B (blue) or Bk (black) is formed on a substrate, for example, as a color filter for a liquid crystal display device or the like, a pattern defect (pattern imperfection) is generated in certain degree of chances due to a small foreign substance in the production process or in the material of the colored pattern. The pattern defect can be classified into a black defect due to adhesion or the like of the small foreign substance or the like and a white defect (color omission defect or pattern missing defect) in which color is missing and appears to be like white. The white defect also occurs when a fouling is removed from the black defect.
The black defect is not only visually recognizable as a back like spot, but can also cause a serious product defect as it is a projecting imperfect portion, in which when the color filter is affixed together with TFT substrate to compose the display panel, the protrusion reaches the TFT substrate and causes short. The white defect should be avoided since even a small defect of several dozen micrometer will shine like a pin hole and be noticeable when the liquid crystal display device is composed and an image is displayed.
Recently, to meet the need of enlarging size of screen of the liquid crystal display device, there is a trend toward enlarging area of colored patterns. In keeping with this trend, it is more likely that the black defect and the white defect will be generated so that the importance to solve such problems is now increasing than ever.
A skill to partially correct the defect portion disclosed in Japanese Patent Laid-open Publication No. Hei. 6-109919 has been established in order to improve yield ratio and not to damage productivity even if the defect portion is generated. The defect correcting device disclosed therein volatilizes the black defect portion by laser and applies a color ultraviolet curable resin onto a color omission portion of a white defect to be cured by ultraviolet ray.
As methods of applying the color ultraviolet curable resin to the white defect portion, there are methods disclosed in the above publication, which are the method dropping paste of necessary amount by a dispenser and the method using an ink jet. There is also a method disclosed in Japanese Patent Laid-open Publication No. Hei. 8-182949, which imparts the color ultraviolet curable resin on the end of a needle-shaped material formed flat end and presses the needle-shaped material to a defect portion. The publication discloses that the method of directly applying the color ultraviolet curable resin using the needle-shaped material is preferable as it is possible to meet even smaller white defects.
However, the correction does not succeed if the ink for forming small colored pattern is used without change. For example, an ink for forming a coloring layer of a color filter by a printing method has problems that when it is applied to a small color omission portion without change, the viscosity is so high that when the ink is lapped over not only the color omission portion but also a normal color pixel portion, it is likely that the overlapped portion becomes a new protrusion.
As for a coloring resist composition used for a photo process to form a colored pattern, for instance, it aims to evenly apply the resist using spin coat etc. When this composition is applied on a defect portion without change, the viscosity is so low that the applied spot is expanded after applying to have larger overlapped area on the normal color pixel portion leading newly to a color mixing defect. In the case that the viscosity is low, especially when it is applied by a needle-shaped medium, there is a problem of having inferior supportability of the ink on the needle.
Meanwhile, Japanese Patent Laid-open Publication No. Hei. 11-142635 discloses a color paste for applying on a color omission portion using a needle-shaped medium (needle-shaped applying measure). However, the color paste has high solvent content that there are problems such as causing inferior physical stability like viscosity or the like of the color paste at the time of preserving and using and having large volume decrease rate even after applying the color paste due to the volatilization of the solvent. When the volume decrease rate is large, it is difficult to sufficiently thicken a layer of the color omission portion where the paste is supplied and necessary to repeatedly apply the paste to have a sufficient layer thickness. Moreover, if the adhesion amount of one time is increased to have the sufficient layer thickness taking the volume decrease rate into account, the paste runs off to surroundings due to its high liquidity thereby causing a problem such as making a new protrusion or color mixing defect. Also as the color paste has high solvent content, a binder resin content in solid content tends to be small. That will lead to a problem that the adhesive strength of applied layer to a substrate after drying is not good. The binder resin of the color paste is mainly made of polyimide precursor. When content of the binder resin in solid content is made larger, the viscosity becomes higher, which leads to a problem that coating property becomes worse.
Also, as black ink for forming a color filter of a black matrix and a black pigment such as a colored resist composition for the black matrix formed by pattern exposure or the like, a carbon black is conventionally and widely used. However, since the black carbon has electrical conductivity, there is a problem that it may have display imperfection when it is used as a pigment of a correcting black ink because a new protrusion is provided at a corrected portion which reaches to an opposed substrate and electric conduction is generated.
There is proposed to obtain a black color by mixing two pigments of complementary colors instead of using the carbon black as a black color pigment, but actually a combination of two pigments which are perfectly complementary does not exist. Even by mixing two pigments which are nearly complementary colors, it was not able to obtain a black color with high optical density as synthetic dispersion makes the transmissivity in a part of visible light region high and showing blueness and redness.